Severe environmental and climatic problems have occurred due to the greenhouse effect caused by a large-scale emission of carbon dioxide all over the world. Meanwhile, as a useful resource, carbon dioxide have been widely used in the fields of chemical engineering, oil recovery, foods, medicines and the like. Therefore, capturing CO2 and then using it in associated fields can not only effectively mitigate climatic problems, but also bring a great economic benefit.
Currently, absorption processes using organic amine solutions are commonly used processes for CO2 capture and recovery, and have been widely applied to natural gases, synthesis gases, flue gases and other source gases. Researchers are continuously working to develop effective absorption solutions in the following ways: 1) increasing the CO2 absorption capacity; 2) improving the anti-corrosion and anti-degradation performances of the solvents; and 3) reducing the energy consumption and the environmental impact. In recent years, studies in countries over the world have made a great progress in the first and third ways. But, studies in the mitigation of oxidative degradation of organic amine solutions are very limited, which become the bottleneck of a further development of such processes.
Chinese Published Patent Application Nos. CN 101053751A, CN 101612509A and CN1381301A disclose the use of copper actate, sulfates, and some other metal oxides or salts as an antioxidant in absorption solutions. These antioxidants belong to oxygen-consuming reagents. In order to compensate the consumption of such antioxidants, a periodical supplementation of fresh antioxidants to the absorption system is required, which not only increases the operating cost, but also introduces impurity ions to the system. And, the accumulation of impurity ions may decrease the decarbonization capacity, i.e., the capacity for absorbing and capturing CO2, of the absorption solution.
Chinese Published Patent Application No. CN 101822932A discloses the use of phenols, such as hydroquinone, p-hydroxyphenol and the like, as an antioxidant. However, such materials have disadvantages of being susceptible to deactivation at elevated temperatures, lack of environmental friendliness, etc.
Chinese Patent Application No. CN1381301A discloses the use of a solid metal oxide and salts thereof as an antioxidant, which shows a good anti-oxidative effect on an aqueous monoethanolamine solution and can greatly extend the working life of the solution. But, such an antioxidant is useful for only a few organic amines.
Japanese Patent No. JP3739437B2 discloses the use of imidazole-based organic sulfur compounds as an oxidation inhibitors for alkanolamines. Although such compounds can greatly inhibit oxidative degradation of alkanolamines, they themselves are also susceptible to oxidation in practical operation conditions in industry.
International Published Patent Application No. WO2011036712A1 discloses the use of a kind of sulfur-comprising amino acids for preventing the oxidation of alkanolamines. But, such materials are also oxygen-consuming oxidation inhibitors in nature.
US Published Patent Application No. US 2004/0253159 A1 discloses a composite antioxidant system comprising (hydro)sulfites, aromatic amines, metal chelating agents, and the like. International Published Patent. Application No. WO2012125894 A2 discloses a kind of antioxidants comprising one or more metal chelating agents, including 1-hydroxyethylidene-1,1-diphosphonic acid, diethylenetriamine pentaacetic acid, diethylenetriamine pentamethylene phosphonic acid, and the like, or salts thereof for capturing metal ions. In these two patent applications, the metal chelating agents are used to capture free metal ions, such as Fe3+, Cu2+, Cr3+, V5+ and Ni2+, present in amine-based solvent systems, so as to inhibit the catalytic oxidation of amines in the presence of the metal ions, thereby greatly mitigating the oxidative degradation reactions of the amine solvents.
US Published Patent Application No. US2009205496A1 discloses a method for inhibiting O2 or SO2 induced amine degradation by using sodium sulfite, sodium potassium tartrate tetrahydrate, ethylenediaminetetraacetie acid, hydroxylamines, and the like, or mixtures thereof, which is reported to show a good inhibitive effect on the degradation.
Till now, most existing antioxidants have the disadvantages of poor anti-oxidative effect, high consumption and/or limited suitability for only a few organic amine systems, etc. A few patent applications, such as US2004/0253159A1 and US2009205496A1, have proposed composite systems comprising chelating agents and sulfites, but sulfites used in such composite systems tend to form SO42− in organic amine systems. And, stable salts thus formed may not only increase the boiling point of the decarbonization solution, thereby increasing energy consumption, but also cause a corrosion effect on pipelines and apparatus. International Published Patent Application No. WO2012/125894A2 is directed to the use of metal chelating agents alone as an antioxidant, of which the anti-oxidative mechanism is simplex and the overall anti-oxidative effect is limited and needs to be further improved. In view of the above, there remains a need for antioxidants or antioxidant systems for organic amine decarbonization solutions, showing wide suitability and good anti-oxidative effects.
All references mentioned in the present application, including but not limited to patents and published patent applications, are incorporated herein by reference to the extent of not conflicting with the present application.